This invention relates to fifth wheel hitches, and particularly to a lock mechanism for a fifth wheel hitch.
Fifth wheel hitches are primarily employed to connect a semitrailer to a towing truck tractor. Several types of fifth wheel hitches have been developed during the twentieth century. One type of hitch is that sometimes known as the "A" type, shown in Ketel U.S. Pat. No. 2,610,069 and marketed by the assignee herein. The swing jaw of that hitch is locked in place by a spring biased plunger when the jaw is fully closed behind the kingpin. This plunger bears against the locking jaw rear surface when in locked position, to prevent the swing jaw from opening.
During use, hitch components such as the jaw elements eventually become somewhat worn to thereby result in some undesirable clearance or play between the kingpin and the hitch jaws. To keep this clearance and resulting play to a reasonable amount, a double wedge adjustment mechanism has been provided to the market by the assignee herein as part of the hitch assembly. Such an adjustment apparatus is shown, for example, in FIG. 6 herein and in U.S. Pat. No. 5,257,796, incorporated herein by reference. The adjustment apparatus has the forward surface of a fixed wedge bearing against the rearward surface of a laterally movable wedge, the movable wedge being adjustable by a threaded bolt or the like, to bear against the locking plunger rear surface with enough force to move it and hold it in the desired position for accommodating wear of the hitch components. The entire apparatus, including the adjustment mechanism, is initially factory adjusted for proper interfit. When wear occurs over a period of time, the adjustable wedge of the hitch is appropriately adjusted by trained authorized maintenance personnel knowledgeable concerning fifth wheel hitch mechanisms, to take up the slack to the desired clearance.
It has been determined that unauthorized persons might irresponsibly adjust the hitch lock mechanism. If the movable wedge member is not adjusted enough, the connection to the kingpin will still have excess clearance remaining and, while that may be annoying to the driver, it does not present a particular problem. However, if the movable wedge is adjusted too much, the lock plunger will be shifted too far toward the swing jaw. When the swing jaw closes, the plunger will abut against the end of the jaw and not be able to slide behind the jaw to lock it. The driver may believe he has secured the hitch, and begin to drive the tractor forwardly, but the hitch jaw will open so the trailer will not be pulled with the tractor and may
Another complication that may result during hitching of a truck tractor to a trailer occurs when the driver engages the tractor fifth wheel hitch to the trailer kingpin at too great a speed. This can result in the trailer being bumped rearwardly so the kingpin is not fully within the throat of the hitch. In this condition, the swing jaw cannot fully close so the lock plunger cannot shift behind the swing jaw to lock it. The driver thus must often repeat the coupling attempt.